Wearing and laundering of fabric articles can result in a discoloration of the fabric articles from the original fabric color. For example, white fabrics which are repeatedly laundered can exhibit a yellowish appearance which makes the fabric look older, stained and/or worn. To overcome the undesirable yellowing of white fabrics, and similar discoloration of other light colored fabrics, it is desirable to formulate a hueing dye in a laundry detergent composition so as to impart a favorable hue to the fabrics by laundering such fabrics in an aqueous solution of the laundry detergent composition.
Hueing dyes used in laundry detergent composition are typically an acid dye, a basic dye or in some cases, a direct dye. However, after repeated laundering of textile with detergent containing such hueing dyes, the hueing dye tends to accumulate on the textile, giving the textile a tint of the dye. For example, repeated laundering of white fabric articles with a laundry detergent composition comprising a blue dye tends to give the articles a bluish, rather than white, appearance. The shades of pastel colored fabrics tend to change as well upon repeated laundering with detergents containing hueing dyes. Hence the use of such dyes tends to present a trade-off between hue benefit and tint accumulation.
Another group of dyes, reactive dyes have been used in the textile manufacturing industry for coloring textiles by covalent bonding to the fabric under conditions like high pH, high temperature and/or high dye concentration, and for ink-jet printing of textiles, but not in the laundry detergent field. Indeed, some prior art, such as WO 2006/027086 teaches that reactive dyes can not be used in a laundry treatment composition, since the functional groups in a reactive dye can allegedly cause irritation/sensitization of respiratory tract and skin. Such prior art, thus teaches to use hydrolysed reactive dyes to impart desired shading to textiles. However, hydrolysed reactive dyes are not as commercially available as the reactive dyes are. Since additional hydrolysation process is needed for preparing the hydrolysed reactive dyes, the cost of hydrolysed reactive dye becomes higher than reactive dye and the quality control of hydrolysed reactive dye is much more complex than that of a reactive dye. In short, application of hydrolysed reactive dyes in laundry detergent compositions is less practical than that of reactive dyes.
Accordingly, a need exists for improved laundry detergent compositions which can impart a favorable hue to fabrics without undesirable accumulation on the fabrics by laundering the fabrics.